Professm^ Geikie on the " Pitchstonc " of Eskdale. 219 



aspera and iTUtchits dorsettensis are only seen in the northern 

 half of the bay, and Fagurics prideatcxii only in the southern 

 half. Among the Molluscs rather a well-marked case is 

 seen in Lima, which is only found in the northern part of 

 the bay, and in greatest abundance off the north end of Holy 

 Isle — about Station 10. 



V. The " Pitchstonc " (Vitreous Basalt) of EsMcde : A Retro- 

 spect and Comparison of Geological Methods. By Archi- 

 bald Geikie, LL.D., F.E.S., Director of the Geological 

 Survey of Scotland, and Murchison Professor of Geology 

 and Mineralogy in the University of Edinburgh. [Plates 

 V. and VL] 



(Read 18th February 1880.) 



Part I. — Eetrospective. 



In a remote pastoral valley among the southern uplands 

 of Scotland a group of green hills rises on the west side of 

 the river Esk, not far from the manse of Eskdalemuir. These 

 eminences, known in the district by the names of Wat 

 Carrick, Watch Craig, and Castle Hill, stand out from among 

 the gentle grassy slopes of the dale with a certain ruggedness, 

 or at least with a broken character of summit, which forms a 

 pleasing relief from the monotony of the surrounding undula- 

 tions. They were introduced to the attention of geologists in 

 the beginning of this century, by Professor Jameson of Edin- 

 burgh,* but since that early date, so far as I am aware, no 

 further geological description of them has been given. As they 

 offer in themselves matter of considerable interest, and since 

 the questions they raise naturally bring out into strong con- 

 trast former and present methods of geological research, I have 

 t bought that in recalling them once more to notice, it might 

 c profitable to offer at the same time a brief review of the 

 state of geology in this country at the date of Jameson's 

 observations, more especially with reference to the interpre- 

 tation of what we now know as igneous rocks. 



* Mineral ogical Description of Dumfriesshire, 8vo, pp. 185, Edinburgh, 

 1805. The Dedication of this work is dated "College of Edinburgh, October 

 10, 1804." 



